Gum recession happens when the gum tissue has receded and lowers its position on the tooth, exposing the roots of the teeth.
You may be at more risk of recession depending on the position of your teeth in the jaw as well as the thickness of your gum and bone. The recession itself may be caused by plaque, overly aggressive brushing or trauma from e.g. lip/tongue piercings.
Gum recession needs attention and the first step is to consult your dentist or a gum expert on whether further measures need to be taken to stop or correct the recession.